Frank Lampard's return to the Stamford Bridge dugout ended in more misery for Chelsea as Brighton & Hove Albion came from behind to win 2-1 in the Premier League.
A deflected Conor Gallagher strike in the first half marked the first goal of Lampard's second stint in charge, but a free-flowing Brighton side responded through Danny Welbeck's header and a phenomenal long-range Julio Enciso winner to continue their assault on the European places.
In strikingly similar fashion to their defeat to Tottenham Hotspur last weekend, Brighton were not rewarded for their early spate of dominance, but not without a healthy dose of controversy.
Alexis Mac Allister sent a couple of early attempts off target before Evan Ferguson struck the bar in the ninth minute, and the Seagulls would be made to pay for their profligacy.
With 14 minutes gone, Mykhaylo Mudryk drove infield from the left and cut back for Gallagher, whose first-time strike from the edge of the box took a significant deflection off Lewis Dunk and looped over the returning Robert Sanchez.
Brighton's reaction to going behind was a typically positive one, but there was a familiar sense of officiating dread for the visiting fans - whose side received a PGMOL apology for a missed spot kick last weekend - and they were denied a strong penalty shout for a Christian Pulisic handball in the 21st minute this time around.
The Seagulls' momentum was briefly halted by an injury to right-back Joel Veltman on the 28-minute mark, and Roberto De Zerbi responded by bringing on another attacker in Enciso, forcing Pascal Gross to right-back in the process.
De Zerbi's men continued to carve open opportunities at will and were inches away from levelling matters in minute 34, but Kepa Arrizabalaga did brilliantly to tip Ferguson's attempt over the bar, and the talented teenage striker then became Brighton's second casualty of the first half - coming off for Welbeck not long after.
Brighton's striker change may have been an enforced one, but it proved to be the catalyst for a deserved equaliser in the 42nd minute, as Gross's inswinging cross towards the back stick met the head of Welbeck, who nodded home off the inside of the post.
The second half started in a similar vein to the first, with Chelsea being forced to quell a barrage of Brighton advances, and the visitors struck the woodwork on the hour mark through Enciso before Welbeck sent the rebound harmlessly over the bar.
Enciso was not to be denied, though, and the Seagulls' super sub turned the game on its head in extraordinary fashion in the 69th minute, receiving Solly March's pass from 30 yards out and taking touch before unleashing a thunderbolt into the top corner.
As was the case at Molineux, Chelsea's toothless attack could not find the answers, and Lampard's side continue to languish in the bottom half in 11th place, while Brighton stay seventh, seven points off the top four.
The Blues now gear up for the second leg of their Champions League quarter-final with Real Madrid - who hold a 2-0 advantage from the first leg - on Tuesday, while the Seagulls are in FA Cup semi-final action against Manchester United next Sunday.
